Tugidak Island, located in the Gulf of Alaska, was once the site of one of largest local concentrations of harbor seals (Phoca vitulina richardsi) in the world. This population, which probably consisted of about 20,500 animals in the mid-1960s declined by about 85% between 1976 and 1988. The population appeared to decline more rapidly during the late 1970s than during the 1980s. Causes for the decline are not apparent. There appear to be both similarities and dissimilarities between this decline and recent declines in abundance of northern fur seals (Callorhinus ursinus) and Steller sea lions (Eumetopias jubatus) in the Bering Sea and Gulf of Alaska.